When comet Linear blew apart in the
summer of 2000, the event underscored the failure of popular comet
theory to anticipate the actual attributes and behavior of comets.
Linear was not the “dirty snowball” of modern comet lore.

In September 1999, the LINEAR telescope in New
Mexico detected a comet out beyond the orbit of Jupiter, speeding toward
the Sun. Because it was the first instrument to see it, the comet
received its name from the telescope.

Linear was estimated to be about a mile wide. As
it approached its perihelion in July 2000, many telescopes—including the
Hubble Space Telescope—had the comet in clear view. Then strange things
began to happen. On July 5, Linear brightened by more than 50 percent in
just four hours. It was throwing off large quantities of dust—much
more dust than the expected water or other volatiles.

Next, a chunk of the nucleus tore away and “blew”
back into the tail where it continued to disintegrate, as can be seen in
the Hubble Space Telescope images here.

Then, on July 14, the orbiting Chandra X-ray
Observatory discovered that the “dirty snowball” was generating X-rays!
(Photo above left).

The mystery of comet X-rays had begun only four
years earlier. It had always been supposed that these “frozen” objects
would exhibit none of the high-energy reactions necessary to produce
X-rays. But then on March 27, 1996, the ROSAT satellite recorded X-rays
on the sunlit side of Comet Hyakutake. A NASA report on Hyakutake notes
that astronomers “were shocked by what they saw. ROSAT images revealed a
crescent-shaped region of X-ray emission around the comet 1000 times
more intense than anyone had predicted!” For four years the source of
the X-rays remained a mystery, as the ROSAT, EUVE and BeppoSAX
satellites detected X-rays and extreme ultraviolet radiation from more
than half-a-dozen comets, including Hale-Bopp.

But now, Linear was giving astronomers some
telling clues, and the implications were electrical.
Chandra viewed the comet Linear repeatedly over a two-hour period. The
Observatory’s press release reported that the X-rays were being produced
“by collisions of ions racing away from the sun (solar wind) with gas in
the comet. In the collision the solar ion captures an electron from a
cometary atom into a high-energy state. The solar ion then kicks out an
X-ray as the electron drops to a lower energy state”. The authors of the
news release do not appear to have known that, in the electric
model of comets, this was a
predictable reaction
between the negatively charged plasma of the comet’s coma and the
positively charged ions in the solar wind—nature’s efficient means of
X-ray production.

As seen in the X-ray image of Linear above, and as
the electric model would anticipate, the X-ray production occurred at
the interface of the negatively charged cometary plasma with the
positively charged particles of the solar wind.

A NASA Science News story on Linear thus reports,
“When ions from the Sun blow past a comet, their strong positive charge
attracts negatively-charged electrons from cometary atoms and molecules.
In effect, the ions try to neutralize their own unbalanced charge by
stealing electrons from the comet”. The report states that electrons
contributed by the comet, in uniting with the positive ions from the
solar wind, “emit X-rays as they cascade from high-energy to low-energy
ionic orbits. This process, called a ‘charge exchange reaction’, was
first proposed in 1997 as a possible reason for cometary X-rays”.

But the NASA report assumes, in contradiction of
evidence gathered for almost twenty years, that it is neutral
atoms in the coma that contribute the electrons. More reasonable
is the contention of the electric theorists that comets are the
cathodes, or negatively charged objects, in an electrical exchange with
the Sun. In this view, excess electrons will combine preferentially with
the positive ions in the solar wind. In fact, the excess of electrons in
a cometary coma was first noted in 1986, when the Giotto spacecraft
detected an abundance of negatively charged atoms in the inner coma of
Comet Halley.

Also, as a matter of historical record, the NASA
statement that “charge exchange reaction” was first proposed in 1997
misses the mark by a century. The electric comet hypothesis has been
around since the nineteenth century. Though it virtually disappeared
from official scientific discussion by 1930, the concept received its
greatest clarity from the contributions of engineer Ralph Juergens
beginning in 1972. Juergens proposed an electric Sun model, along with
the corollary that cometary comas and tails are produced by an
electrical exchange between the Sun and the comet. Later, in the early
80’s, physicist James McCanney set forth his own version of the electric
comet. He predicted that comets would be found to emit X-rays.

Comet Linear had more evidence to present. As the
comet neared its perihelion or closest approach to the Sun—about 114
million kilometers (70 million miles) from the Sun, or three quarters of
the distance from the Sun to Earth—astronomer Mark Kidger was observing
Linear with the Jacobus Kapteyn Telescope at La Palma in the Canary
Islands. He noted something strange. The normal teardrop shape of the
coma was undergoing an unexpected metamorphosis. Over several nights he
watched the comet elongate into a "cigar" shape. Kidger soon realized
that the nucleus of Linear was breaking apart—and catastrophically. This
was not merely a fragmentation of the comet into separate visible
pieces. The comet was dissolving in front of his eyes.

“Comet LINEAR seems to be dissolving into an
amorphous haze of gas and dust”, exclaimed a NASA Express Science News
release. “The break-up of Comet Linear as it swept past the sun last
week has shocked astronomers into rethinking theories of the origins of
such rocky ice balls”, reported Space.com on August 4, 2000.

How did this happen? A NASA release of July 31,
2000, reports that, “Intense solar heating apparently triggered a
massive disruption of the comet's fragile icy core when it passed close
to the Sun”. Kidger suggested the same thing, invoking “intense heating”
and “thermal stresses” on the comet. But it is not reasonable to assume
that a mile-size ice chunk would explode in space under something as
mild as solar radiation millions of miles from the Sun. As an icy body
sublimates in the Sun, it cannot even convey heat a few inches into its
interior. An explosion due to heating, involving extreme forces deep
within a body, is unthinkable.

Many comet watchers began to consider seriously
whether comets are actually loosely aggregated collections of
"mini-comets", permitting them to fly apart when disturbed. Some began
to speak of Linear as an aggregation of cosmic fluff—a “wimpy fluff
ball”, as astronomer Donald Yeomans put it.

But prior picture of the comets Halley and
Borrelly—and most recently of comet
Wild 2—make
clear that comet nuclei are solid objects. It was the Stardust mission
to Wild 2 that produced the best pictures ever of a comet nucleus. It
showed a well-defined and cratered surface with no indications of
separate objects held in a flimsy aggregation.

More details on comet nuclei will be forthcoming
soon, when the
Deep Impactmission fires a 370 kilogram copper projectile into the nucleus
of Comet Tempel 1. The event is scheduled for July 4.

In the electric model of comets, there is nothing
unexpected in an explosive demise. As a comet moves through the radial
electric field of the Sun, approaching perihelion, the nucleus suffers
the maximum electrical stress. This usually results in an increase in
brightness of the nucleus due to a larger number of cathode arcs
operating simultaneously, explosively removing solid material from the
nucleus and accelerating it into space to form the dust tail. Both of
these conditions were noted in the case of Comet Linear, suggesting that
the comet was progressing toward an internal discharge.

A comet nucleus can be compared to the insulating
material in a capacitor. As charge is exchanged from the comet’s surface
to the solar wind, electrical energy is stored in the nucleus in the
form of charge polarization. This can easily build up intense mechanical
stress in the comet nucleus, which may be released catastrophically, as
in a capacitor when its insulation suffers rapid breakdown. The comet
will explode!

As suggested by electrical theorist Wallace
Thornhill, “comets break up not because they are chunks of ice ‘warming’
in the Sun, and not because they are aggregations of smaller bodies, but
because of electrical discharge within the nucleus itself”.

There were more surprises. Perhaps the greatest
shock came from analysis of the debris left by the comet’s dissolution.
According to Hal Weaver, an astronomer at Johns Hopkins University in
Baltimore (as reported in an AP story on May 18, 2001), researchers were
“surprised at the ratio of ice to dust and rock in Linear”. Analysis
showed that Linear “had about 100 times more solid rock and dust than
ice”.

But the problem of missing water on the nucleus of
comets is as old as the Giotto probe of Comet Halley, which could not
find any definitive evidence of water but did find evidence
against the presence of water. No water could be found on the
nucleus of comet Borrelly. When comet
Shoemaker-Levy 9
broke apart, astronomers reasoned that the fractured nucleus would
expose fresh ices that would sublimate furiously. So several
ground-based telescopes and the Hubble Space Telescope trained their
spectroscopes on the tails of the fragments of SL-9, looking for traces
of volatile gases. None of the gases was found.

Events and observations surrounding the breakup of
Comet Linear thus offer many pointers to the true electrical nature of
cometary intruders. Comets may or may not possess volatiles, and we can
be confident that comets exhibit much more than sublimating ices. Only
electric discharge will account for the full range of new data on
comets.